This study is to assess the anti-hypertensive effect of single oral dose of an antivasopressor v1 vasopressin (avp) antagonist. Because our previous research over the past 10 years has shown that vasopressor role of avp is maximal in black hypertensives with pre-existing sympathetic inhibition, we plan to enroll black hypertensives in this trial and pretreat them with the sympatholytic drug clonidine prior to administration of the experimental drug.